Game-Changer: Breakthrough Mercedes Gasoline Engine Uses Less Fuel Than Diesels

 DiesOtto: A gasoline engine with diesel genes. 
(Photo: DaimlerChrysler)STUTTGART, GERMANY (August 6, 2007) - New data released by Mercedes-Benz on its advanced technology 1.8L DiesOtto gasoline engine reveals the fuel consumption impact of breakthrough technology that combines diesel and gasoline engine features.  The DiesOtto name is derived from the respective engine inventors' names - Rudolf Diesel and Nicholas Otto - whose basic technologies have been combined by Mercedes in an advanced example of drastic engine downsizing supported by a number of added systems. Historians will note that the DiesOtto development comes from Mercedes which traces its origin back to the beginning of the internal combustion engine powered automobiles of Gotleib Daimler, Wilhelm Maybach and Karl Benz. In a demonstration, Mercedes-Benz used three otherwise equal S-class cars for a demonstration: one fitted with a conventional 3.6L gasoline engine, one with a 3.0L diesel engine and the third with the new 1.8L DiesOtto engine. Expressed in US mpg terms, DiesOtto improves mileage in the same vehicle by 72 percent vs. the conventional gasoline engine and 41 percent vs. the same vehicle equipped with a conventional diesel powertrain.  Fuel consumption data expressed in liters/100 km along with KW power:EngineFuel ConsumptionKilowatt  Power3.6L gasoline engine10.3 liters/100 km200 KW3.0L diesel engine8.5 liters/100 km173 KW1.8L DiesOtto gasoline engine175 + 15 (ISG) KW

Engine displacement is cut virtually in half to gain higher efficiency at moderate load conditions . In-series twin turbocharging is employed to achieve high power when needed. Other systems integrated into the DiesOtto engine to boost the fuel efficiency include variable valve actuation, piezo type direct fuel injection and variable compression ratio along with "controlled auto ignition" (often called HCCI - homogenous charge compression ignition). 

Mercedes-Benz says that while the new engine requires premium grade gasoline, its efficiency more than offsets the cost. In addition, conventional gasoline exhaust aftertreatment systems are used rather than diesel emissions controls. Adding to the importance of Mercedes' achievement is the fact that gasoline contains about 11 percent less energy per gallon than diesel fuel; hence, on a thermal efficiency basis, the DiesOtto performance gain is particularly significant.

The fuel economy improvement also reflects the inclusion of its innovative Integrated Starter Generator (ISG) - an automatic stop/start system that shuts the engine down when the vehicle is stopped in urban conditions. Mercedes says this accounts for 10 percent of the efficiency gain and adds 15 percent to power. This and the various other enhancements in the DiesOtto system are to be phased into other production vehicles over time. 

Mercedes has indicated it will release more detail about the engine's operational characteristics, its deployment schedule and perhaps give an indication of the degree to which fuel consumption is even less than 6 liters/100 km at the coming Frankfurt auto show this September.

For now, the degree to which DiesOtto gasoline engine technology has exceeded the energy efficiency of both conventional gasoline and diesel systems, has all the earmarks of a major milestone. And since DaimlerChrysler is a member of the HEDGE consortium of engine and vehicle companies, it will be asked to what degree HEDGE technology may be employed in the DiesOtto system..

For now a central question will be how DiesOtto cost will compare with current technology and to what extend its overall economics will permit use in both smaller cars and heavier commercial vehicles. For vehicles that are used mostly at highway speeds, the added cost of the DiesOtto system could be the better choice compared with hybrids. The high efficiency of DiesOtto technology combined with stop/start technology may also compete with traditional hybrids in city conditions.